Preparation of 1, 1-difluoroethane



April 8, 1958 F. w. SWAMER 2,830,099

' PREPARATION OF 1,1-DIFLUOROETHANE Filed April 6, '1956 FIG.L

26 24 CONDENSER COOLING WATER'L, CATALYSTW HYDROGEN FLUORIDE INPUT INPUT 1/ 4 22 FIG 2 |4 4 as 34 3s 4o }:2- ACETYLENE PRODUCT we COOLING JACKET lo moron coounc ,42 WATER v g7 L HYDROGEN FLUORWE 1; PLUS CATALYST ACETYLENE INPUT INVENTOR FREDERIC W. SWAMER ATTORNEY United States Patent 2,830,099 Patented Apr. 3 1958 2,830,099 7 PREPARATION OF 1,1-DlFLUOROETHANE Frederic W. Swamer, Boothwyn, Pa., assignor to E. I. du Pont 'de Nemours'and Company, Wilmington, 9:21., a corporation of Delaware 7 Application April 6, 1956, Serial No. 576,571

12 Claims. (Cl. 260-653) This invention relates to the preparation of 1,1-difluoroethane, and more particularly to an improved process for its preparation by'the reaction of hydrogen fluoride with acetylene in the presence of a novel catalyst for the reaction.

It is known that 1,1-difluoroethane is valuable as a refrigerant, as a solvent, and particularly as an intermediate for the production of vinyl fluoride which is known to be a valuable polymerizable material. Vinyl fluoride can be readily prepared by passing 1,1-difluoroethane over a heated catalyst bed, such as aluminum sulfate, to split oif HF When carrying out this dehydrofluorination process, it has been found that as little as 1% of vinyl fluoride in the 1,1-difluoroethane materially shortens the life of the catalyst and thus renders the dehydrofluorination process ineflicient.

It has long been known that 1,1-difluoroeth-ane can be prepared by the reaction of acetylene with hydrogen fluoride (HF), usually in the presence of a catalyst. In most cases, vinyl fluoride is simultaneously produced in material proportions, frequently equal to or exceeding the amounts of 1,1-difluoroethane. Such mixtures require costly separation steps in order to obtain the 1,1-difluoroethane sufliciently pure for most purposes, including efficient use in the process for its conversion to vinyl fluoride. Also, such catalysts generally must be employed in large concentrations, have short catalyst lives, require high temperatures and/ or pressures, and frequently are quite costly. These features materially increase the cost of the process and of the product.

Burke et al., in Patent No. 2,425,991, have shown that 1,1-difluoroethane can be obtained substantially free of vinyl fluoride by reacting acetylene with liquid HF containing boron trifluoride as the catalyst. However, this process suffers from the disadvantage that the boron trih fluoride is quite volatile and, in continuous processes,

must be continuously replaced. Also, because of its cost and the large amounts generally used, the boron trifiuoride must be recovered for reuse. Thus, the use of boron trifluoride as the catalyst also makes for a generally expensive process.

It is an object of this invention to provide a novel process for producing 1,1-difluoroethane by the reaction of acetylene and hydrogen fluoride. Another object is to provide such a process wherein 1,1-difluoroethane is obtained substantially free of vinyl fluoride. A further object is to provide such a process employing a novel catalyst which is cheap, is effective in small concentrations, and does not require recovery for reuse. A still further object is to provide such a process employing such a catalyst at low or moderate temperatures and pressures. A particular object is to provide a continuous process for the preparation of substantially pure 1,1-difluoroethane from acetylene and liquid hydrogen fluoride. Still another object is to provide an inexpensive process for preparing 1,1-difluoroethane from acetylene and hydrogen fluoride, which process is simple and is readily operated and controlled. Other objects will appear. hereinafter.

The above and other objects may be accomplished according to this invention which comprises dissolving anhydrous stannic chloride in a concentration of from 0.1% to about 5% by weight in substantiallypure liquid hydrogen fluoride (HF), then passing gaseous acetylene free of catalyst poisons into the solution while maintaining the solution at a temperature of from about 0 C. to about 65 C. and at a pressure .of from 0 to about p. s. i. gauge suflicient to maintain the HP in the liquid state at the temperature employed.

'It has been found that by such process LI-difluoroethane is obtained efliciently in excellent yields substantially free of vinyl fluoride and hydrogen fluoride and requires a minimum of after treatment to obtain 1,1-difluoroethane in sufliciently pure form for most purposes. The catalyst is not volatile, is unusually etfective in small concentrations, is inexpensive, does not require recovery, has an unique catalystlife in excess of 12 hours and an exceptional catalyst yield considerably in excess of pounds of 1,1-difluoroethane per pound of catalyst. During the reaction process, only insignificant amounts of tars, gums and other unwanted products are found. These factors, together with the low or moderate temperatures and pressures employed, contribute to the economy of the process,j resulting in a very inexpensive process and the production of 1,1-difluoroethane at low cost.

The process may be carried out batch-wise or in a 7 with the catalyst, and it is usually necessaryto employ excess acetylene which then appears in the product and must be separated therefrom.

Apparatus suitable for carrying out the process of this invention is illustrated diagrammatically in the accompanying drawings in which:

Figure 1 is representative of one type of reaction systern suitable for carrying out the reaction on a continuous manner; and Figure 2 is representative of a s'econdbut less preferred type of reaction system suitable for carrying out the, reaction as a batch or a continuous process.

Referring first to Figure 1, the reactor 10 consists of a vertical tube 30 incheslong and A2 inch-inside diameter which is made of a material which is inert to the reactants and to the reaction products, such as stainless steel or a solid polymeric material of the character of polyclilorotrifluoroethylene, polyethylene, and poly'tetrafluomethylene. The reactor is closed at the bottom by a drain off valve 12and at the top by a valve 14 connected with a catalyst input line 16, and is surrounded by a glass cooling jacket 18. An acetylene input line 20, suitably inch stainless steel tubing, is connected with the lower end of the reactor. A line 22, suitably-of stainless steel tubing, leads off from the top of thereactor to the lower end of a stainless steel condenser tube 24 and beyond to form an input line for liquid hydrogen fluoride. The condenser tube is surrounded by a coolingjacket 26 and is connected at the top with a difluoroe'thane exit line 28.

In operation, the condenser and the reactor tubes are cleaned by rinsing several times with anhydrous hydrogen fluoride. The system is then purged with nitrogen. The

- metal halide is introduced into the reactor tube and substantially pure, liquid anhydrous hydrogen fluoride is added and dissolves the metal halide. A cooling fluid, usually Water, is circulated through the jacket 18 to maintain the solution at the desired temperature. Also, a cooling fluid is circulated through the jacket 26 to maintain the condenser at a temperature to condense any vaporized hydrogen fluoride, but not the LI-difluoroethane,

The gaseous acetylene is then forced through line 20 and into the solutionin the reactor tube at the desired rate where it rapidly reacts with the liquid hydrogen fluoride... The 1,1-difluoroethane is somewhat soluble in the liquid hydrogen fluoride and does not issue from the solution until the solution becomes saturated with it. Since 1,1-difluoroethane passing out of the liquid HF will pre.

vent the drop in pressure. Therefore, the introduction of the inert gas is then discontinued and only pure gaseous acetylene is passed through line 20. The, efflu'ent gases from the reactor tube pass into the condenser where vaporized hydrogen fluoride is condensed and flows back into the reactor tube. The gases flow through the condenser tubeand out through line 28 to a vessel (not shown) containing aqueous sodium hydroxide solution where they are scrubbed with such solution to remove any .traces of entrained hydrogen fluoride carried over by them. Until the amount of 1,1-difluroethane produced exceeds the amount that will dissolve in the liquid HF, the gases willbe composed almost entirely of nitrogen. Thereaftenthe gases will be composed largely of 1,1-difluoroethane, the amount of nitrogen therein decreasing rapidly after the flow of nitrogen to the system is discontinued. Substantially pure liquid hydrogen fluoride is continuously introduced into the reactor tube through line 22 at a rate equalto that at which it is removed from the solution in the reactor tube as by reaction to produce the 1,1-difluoroethane. 4

Referringmore particularly to Figure 2, the reactor vessel is in the form of a bottle having a capacity of about 500 ml. and made of a material which is inert to the reactants and to the reaction products, such as polyethylene, poly-chlorotrifluoroethylene, and polytetrafluoroethylene. The top of the reactor vessel is closed by a stopper or screw cap 32. The cap, 32 is provided with a gas inlet tube 34 provided with a valve 36. The tube 34 may terminateat the inside wall ofthe cap, but, preferably, extends nearly to the bottom of the reactor vessel 30 as shown. Thecap 32 is also provided with a gas outlet tube 38 provided with a.valve and, preferably,. .also connected to a reflux condenser similar to that of Figure 1 (notshown inFigure 2). Preferably, the reaction vessel will be set in or surrounded by a bath (not shown) of a cooling liquid, such as cold water, to maintain it at the desired temperature. In operation, the. reactor system is carefully dried and purged with nitrogen. The reactor vessel is partially filled with substantially pure, liquid anhydrous hydrogen fluoride, as to line 42. Conveniently, this is accomplished by forcing anhydrous HF into the vessel cooled to about 78 C. by a bath of Dry Ice and acetone. The metal halide is added and dissolved in the liquid hydrogen fluoride. The reactor and its contents are permitted to come up to the desired temperature of from about 0 C. to about 65 C., preferably near 0 C. Then acetylene is passed through the solution and the exit gases are passed through a condenser, to condense vaporized hydrogen fluoride and return it to the reaction vessel, and then through aqueous sodium hydroxide. Alternatively, where the acetylene inlet tube 34 does not extend into the solution, the reaction vessel is pressured with acetylene and the solution is agitated as by stirring or by rocking or shaking the reaction vessel, repressuring with acetylene if necessary, until absorption of the acetylene ceases, usually about 3. hours. Then, the contents of the reaction vessel are removed and the 1,1-difluoroethane is separated from the gasesby known methods, In this procedure, it is preferable to use an sulfur dioxide.

excess of acetylene to maintain the desired pressure. The excess acetylene is readily separated from the product by conventional distillation techniques.

It is essential that the anhydrous metal chloride of this invention be added to the liquid HF before the acetylene is passed into it. The addition of the anhydrous metal chloride to the liquid HFwhile the acetylene is being passed into or through the liquid HF, fails to produce the desired results. When the metal chloride dissolves in the liquid HF, part of the chlorine is replaced by fluorine, apparently, to produce complex mixtures of metal chloride, metal fluoride, and metal chlorofluorides, the exact composition of the active catalyst being unknown. The metal chloride may be added to the HF which is to be fed into the reactor.

The amount of the metal chloride added to the liquid HF should be such as to provide a concentration of from 0.1% to about 5% by weight based on the liquid HF, preferably between 0.1% and about 1.0%. These small amounts of metal chloride make for aneflicient and inexpensive process. Larger concentrations of metal chloride, materially above 5%, although operable, are unfor the catalysts of this invention. If significant amounts of these catalyst poisons are present, larger amounts of catalyst will be required to use them up before the catalyst can function and, if they are present in relatively large amounts as in a poor quality crude HF, even large amounts of catalysts are ineffective. Therefore, it is essential that the metal chloride be anhydrous and that the acetylene be free of water and acetone. Acetylene is frequently dissolved in acetone for storage, but is readily freed therefrom by fractionation, scrubbing with aqueous bisulfite, and drying. Neither the metal chloride nor the acetylene ordinarily contains sulfur dioxide. However, crude hydrogen fluoride frequently contains significant amounts of both water and sulfur dioxide. Accordingly, the hydrogen fluoride used in this process must be substantially pure, that is, it must contain less than 0.01% by weight of water and less than 0.1% by weight of Hydrogen fluoride of the required purity can be readily obtained by distilling commercial hydrogen fluoride.

If desired, the gaseous acetylene may be diluted with an inert gas, such as nitrogen, helium, neon, argon, and the like, which has a boiling point materially different from that of the 1,1-difluoroethane so that it can be readily separated therefrom, as by distillation. Usually, such inert gas is not preferred, except in the initial stages of the continuous process where the equipment design is such that a pressure drop is undesirable, i. e., where the pressure drop would tend to cause a caustic scrubbing liquid or other undesirable material to be sucked back fluoride in the liquid state at the temperature employed.

Hydrogen fluoride has a vapor pressure substantially equal to atmospheric pressure at 20 C., of 14 p. s. i. gauge at 40 C., and of 45 p. s. i. gauge at 65 C. and the pressure I in the reactor must be equal to at least those pressures at the respective temperatures. Usually, the pressures will be in the range of 0 p. s. i. gauge (atmospheric pressure) to about p. s. i. gauge. Preferably,'operating at between 0 and 20 C., the pressure will be about at- Therefore, the temperatures. and pressures thospheric pressure. The process can, if desired, be carried out at pressures materially above the vapor pressure of the hydrogen fluoride at the temperature employed. In such cases, it is preferred to employ pressures of from about to about 75 p. s. i. gauge above the respective vapor pressure, but not in excess of 100 p. s. i. gauge.

The time of contact of the acetylene with the solution of the catalyst in the liquid HF is not critical and may be vvariedwidely, but is primarily a function of the method employed for dispersing the gaseous acetylene in the solution. For example, in a continuous process where immediate intimate contact is ensured, the contact time may be 1 second or less. process where there is less eflicient contact,,the contact time may extend to 3 or 4 hours and is governed by considerations of economy. Excess contact time is not harmful because the 1,1-difluoroethane is not affected by the catalyst, the hydrogen fluoride or the'acetylene under the reaction conditions of this invention.

In order to more clearly illustrate this invention, pre-.

ferred modes of carrying it into effect, and the advantageous results to be obtained thereby, the following examples aregiven wherein the parts are by weight except where specifically stated otherwise.

Example 1 i at 12 to C. was pumped through the outer jacket to maintain the liquid HP at this temperature. The system was purged with nitrogen. Pure gaseous acetylene was then introduced to the solution of catalyst in liquid hydrogen fluoride at a rate of 40 cc. per minute, while maintaining the system at substantially atmospheric pressure and replacing the liquid HF as itwasconsumed in the reaction. The eflluent product gases were passed through the condenser and then scrubbed with a sodium hydroxide solution During the 4%. hour operation period, eflluent gas samples were intermittently analyzed. The product was found by analyses to be substantially'pure1,1-difluoroethane which contained neither acetylene, HF, nor vinyl fluoride, the first samples containing the nitrogen that was left in the system from the purging. A yield of 100% 1,1- difluoroethane based on the acetylene feed was obtained.

When the rate of flow of the acetylene into the liquid hydrogen fluoride was increased up to the maximum possible with this equipment, it was found that it was completely-converted to 1,1-difluoroethane, and no acetylene was found in the product.

Example 2 Example 1 was repeated, except that .the stannic chloride was used at a concentration of 0.14% based on the weight of the anhydrous HF. The 1,1-difluoroethane was obtained in excellent yield and neither HF, vinyl fluoride nor acetylene was observed to be present.

Example 3 Example 1 was repeated, except that the reaction temperature was 0 C., and essentially the same results were obtained.

Example 4 Example 1 was repeated, using a catalyst concentration of 0.6% by weight'of the HP. The process was operated for6 hours at a catalyst yield of 100 lbs. of 'l,1-difluoroethane per pound of catalyst.

(This represents a catalyst con- On the other hand, in a batch 6 Example 5 Apparatus, corresponding'to that of Figure 2,was used in which the bottle 30 was constructed of polyethylene and the gas inlet tube 34 reached nearly to the bottom of the bottle.

The bottle was carefully dried and purged with .nitrogen. Then about 100 ml. of substantially pure HF was condensed into the bottle and about 1.5 ml. of anhydrous stannic chloride was added. Pure gaseous'acetylene was passed through the solution at a rate of 50 cc. of gas per minute and at about 10 C. The exit gases from the bottle were passed through a'reflux condenser, scrubbed with a 4% aqueous solution of sodium hydroxide, and then dried. Two gas samples so obtained had the following percent composition:

Component Sample Sample No. 1 No. 2

1,1-difluoroethane 31. 0 47. 2 vinyl fluoride 0. 2 0. 3 ethylene O. 6 air 0. 2 acetylene 63. 6 51. 9 nitrogen 5.0

The following examples are given for purposes of comparison.

Example 6 Example 1 was repeated, except that the reactor tube 10 was constructed of polyethylene and 0.1 part of anhydrous ferric chloride was used in place of themetal chloride'of Example 1. Fourgas samples taken showed the-following analysis (by infrared):

Component Sample Sample Sample Sample o.1 No.2 .No.3 No.4

1,1-difluoroethane 0.3 0.2 0 1 o. vlny1fluoride 0.2 0 7 acetylene 0.2 34.0 5 97. nitrogen 99.5 6546 3 7 1.

Example 7 Example was-repeated, with 0.1 part of anhydrous 'Example 6 was repeated, using 0.1 part of antimony trifluoride in place of the ferric chloride. Three gas samples were taken- They showed the following analysis:

Component Sample Sample Sample No.1 No.2 No.3

1,1-difiuoroethane 0.4 0. 7 0. 7 vinyl fluoride 1. 2 1. 3 1. 2 acetylene 91. 8 97. 6 97. 8 nitrogen 6. 6 0. 4 ,0. 3

The above examples, 6 to 8 inclusive, show'that other metal chlorides and fluorides are not equivalent of the metal chloride of this invention and do not produce like results in the process of this invention. The other metal chlorides and fluorides produce far-lower conversions and yields of 1,1-difluoroethane and the 1,1-difluoroethane constitutes a minor proportion. of the products'and is The r mixed with large proportions of vinyl fluoride and acetylene from which it must be separated in order to hemefol for most purposes. Thus, the other metal chlorides and fluorides are far less efiicient and render the process quite expensive. I

It will be understood that the apparatus disclosed herein and in the'drawings are merely illustrative of the types can be made therein within the scope of the general disclosure, such as in the concentration of the catalyst, the temperatures and pressures, and the techniques employed, without departing from thespirit or scope of, this invention. a

From the preceding description, it will be apparent that this invention provides anovel process for producing 1,1-difluoroethane, employing a novel advantageous catalyst under novel and advantageous conditions, whereby the 1,1-difluoroethane is produced in unusually high yields and in a high state of purity. The catalyst'is cheap, highly efiicient, has a long catalyst life and a high catalyst yield, and is not volatile under the conditions of use. The process is simple, eflicient, easy to operate and control, and exceptionally economical. Therefore, it is apparent that this invention constitutes a valuable advance in and contribution to the art.

The embodiments of the invention in which an exelusive property or privilege is claimed are defined as follows.

I-claim:

1.' The process for making 1,1-difiuoroethane which comprises dissolving anhydrous stannic chloride in a concentration of from 0.1% to about 5% byweight'in substantially pure. liquid HFfand jthen passinggaseous acetylene free of catalyst poisons into the solution while maintaining the solution at a temperature of from about C. to about 65 C. and under a pressure of from 0 to about 75 p. s. i. gauge suflicient to maintain the HP in the liquid state at the temperature employed.

2. The process for making 1,-1.-diiluoroethane which comprises dissolving anhydrous stannic chloride in a concentration of from 0.1% to about 5% by weight in substantially pure liquid HF, and then passinggaseous acetylene free of catalyst poisons into the solution while maintaining the solution 'at atemperature of from about 0 C. to about 65 C. and under a pressureof from about to about 75p. s. i. gauge above the vapor pressure of the HF at the temperature employed but less than 100 p. s. i gauge.

3. The process for making l,l-difluoroethane which comprisesdissolving anhydrous stannic chloride in a concentrationoflfrom 0.1% to about 5% by weight in substantially pure liquid HF, and then passing gaseous acetylene .free of catalyst poisons into'the solution while maintaining the solution at atemperature of from about 0 C. to about 30 C. and under a pressure of from 0 to about 75 p. s. i. gauge suflicient to maintain the HF in the liquid state at the temperature employed.

. 8 acetylene free of catalyst poisons into the solution while maintaining the solution at a temperature of from about 0 C. to about 65 C. and under a pressure of from 0 to about p. s. i. gauge sufficient to maintainthe HF in the liquid state at the temperature employed.

6. The process for making 1,1-difluoroethane which comprises dissolving anhydrous stannic chloride in a concentration of from 0.1% to about 1% by weight in substantially pure liquid HF, and then passing gaseous acetylencfree of catalyst poisons into the solutionwhile maintaining the solution at a temperature of from about 0 C. to about 65 C. and under a pressure of from about 10 to about 75 p. s. i. gauge above the vapor pressure ofthe HF at the temperature employed but less than ps. i. gauge. a

7. The process for making 1,1-difluoroethane which comprises dissolving anhydrous stannic chloride in a concentration of from 0.1% to about 1% by. weight in substantially pure liquid HF, and then passing gaseous acetylene free of catalyst poisons into the solution while maintaining the solution at a temperature of from about 0 C. to about 30 C. and under a pressure of from 0 to about 75 p. s. i. gauge sufficient to maintain the HF in the liquid state at the temperature employed.

8. The process for making 1,1-difiuoroethane which comprises dissolving anhydrous stannic chloride in a concentration of from 0.1% to about 1% by weight in substantially pure liquid HP, and then passing gaseous acetylene free of catalyst poisons into the solution while maintaining the solution at a temperature between 0 C. and 20 'C. and at about atmospheric pressure.

9. The continuous process for making 1,1-difluoroethane which comprises maintaining in a reaction zone a body of a liquid solution obtained by dissolving in a concentration of from 0.1% to about.5% by weight anhydrous stannic chloride 'in substantially pure liquid 1 HF, continuously passing gaseous acetylene free of catalyst poisons into said solution while maintaining the solutionat a temperature of from about 0 C. to about 65 C. and under a pressure of from 0 toabout 75 p. s. i.

gauge suificient to maintain the HP in the liquid state concentration of from 0.1% to about 5% by weight anhydrous stannic chloride in substantially pure liquid HF, continuously passing gaseous acetylene free of catalyst poisons into said solution While maintaining the solution eta-temperature of from about 0 C. to about 30 C. and under a pressure of from 0 to about 75 p. s. i. gauge sufficient to maintain the HF in the liquid state at the temperature employed, and continuously adding to said solution substantially pure liquid HF at a rate equal to that at which it is removed from the solution by reaction with the acetylene.

11. The continuous process for making 1,1-difluoroethane which comprises maintaining in a reaction zone a body of a liquid solution obtained by dissolving in a concentration of from 0.1% to about 5% by'weight anhydrous stannic chloride in substantially pure liquid HF, continuously passing gaseous acetylene free of cataiyst poisons into said solution while maintaining the solution at a temperature between 0 C. and 20 C. and

at about atmospheric pressure, and continuously adding to said solution substantially pure liquid HF at a rate equal to that at which it is removed from the solution by reaction with the acetylene.

12. The continuous process for making 1,1-difluoroethane which comprises maintaining in a reaction zone a body of a liquid solution obtained by dissolving in a concentration of from 0.1% to about 1% by weight anhydrous stannic chloride in substantially pure liquid HF, continuously passing gaseous acetylene free of catalyst poisons into said solution while maintaining the solution at a temperature between 0 C. and 20 C. and at about atmospheric pressure, and continuously adding to said solution substantially pure liquid HP at a rate equal to that at which is it removed from the solution by reaction with the acetylene.

UNITED STATES PATENTS Soll May 31, 1938 Chapman et a1 Jan. 24, 1950 Padgitt et al. Sept. 19, 1950 Skiles Aug. 23, 1955 

1. THE PROCESS FOR MAKING 1,1-DIFLUOROETHANE WHICH COMPRISES DISSOLVING ANHYDROUS STANNIC CHLORIDE IN A CONCENTRATION OF FROM 0.1% TO ABOUT 5% BY WEIGHT IN SUBSTANTIALLY PURE LIQUID HF, AND THEN PASSING GASEOUS ACETYLENE FREE OF CATALYST POISONS INTO THE SOLUTION WHILE MAINTAINING THE SOLUTION AT A TEMPERATURE OF ABOUT 0*C. TO ABOUT 65*C. AND UNDER A PRESSURE OF FROM 0 TO ABOUT 75 P. S. I. GAUGE SUFFICIENT TO MAINTAIN THE HF IN THE LIQUID STATE AT THE TEMPERATURE EMPLOYED. 